Molecular Attraction. 631 



the average tran stationed energy of gaseous and liquid molecules 

 of the same temperature must be equal. 



Now a study of the specific heat of gases showed that the 

 total energy of a gaseous molecule, exclusive of the energy 

 which holds the molecule together and of extraneous forces, 

 is proportional to the translational energy. When the causes 

 for this relation were considered, it seemed a reasonable 

 inference that the corresponding portion of the energy of a 

 molecule of a liqidd would similarly be found to be proportional 

 to its translational energy. Therefore the first assumption 

 follows *. 



The second assumption was made because all of the 

 attractive forces, whose law of variation with the distance is 

 known, obey the inverse square law. This is true of 

 electrical, magnetic, and gravitational forces. Also the 

 intensity of sound, of light, and of heat, vary inversely as 

 the square of the distance from the origin. It seemed to 

 the author, whatever the nature of the molecular attractive 

 force — be it wave-motion or emanation — that the intensity 

 of the force must decrease directly in proportion to the 

 increase in the surface of the wave or emanation front, and 

 since and because this surface increases as the square of its 

 distance from the origin, the attractive force must decrease 

 proportionately, and therefore obey the inverse square law j\ 



The third assumption that the molecular attractive force 

 did not vary with the temperature seemed the most natural 

 assumption, for none of the other attractive forces, chemical, 

 magnetic, electrical, or gravitational, are affected by tempera- 

 ture changes so far as is known. 



The fourth assumption that the molecules in the liquid and 

 in the gaseous condition are evenly distributed throughout 

 the space occupied by them is probably always more or less 

 untrue. But if the molecules are shifted from their ideal 

 position by reason of the attractive force, the particles would 

 gain in kinetic energy exactly so much as they would lose 

 in potential energy. It is possible therefore, without error, 



* The liquid molecules may conceivably possess a " concealed " 

 energy not possessed by the gaseous molecules. If such energy exists 

 it is surrendered in proportion to the internal heat of vaporization, and 

 its effect is cancelled so far as the conclusions here drawn are con- 

 cerned. The evidence upon this point will be discussed in a subsequent 

 paper. 



f I do not intend, however, by this statement to be understood as 

 implying that the reason given is the sole reason for the inverse square 

 law. The neutralization of the attraction may be another factor tending 

 to produce the law. And yet other factors may exist. 1 am not now 

 trying to explain the mechanism, of. the attraction or of its neutral- 

 ization. 



